336 
INSTINCT OF APPETITE. 
shaken to break the bottle and liberate the bromine vapour, 
which immediately decomposes any iodide of silver, setting- 
free the violet vapours of iodine. These condense in the cold 
part of the tube, and may be dissolved out by alcohol. The 
amount of iodine may be estimated by a standard solution of 
sulphurous acid, and the hydriodic acid may afterwards be 
reconverted into iodide of silver and weighed. The process 
gives very exact results ; as it is conducted in a sealed vessel, 
no loss is experienced. 
THE INSTINCT OE APPETITE. 
Chemical analysis and physiological research have esta¬ 
blished beyond dispute that every article of food and drink 
is composed of elements differing in quantity or quality. It 
is equall} r true that the various parts of the human frame are 
different in their composition, as the bone, the flesh, the nerve, 
the tendon, &c. But there is no element in the human body 
which is not found in some article of food or drink. A cer¬ 
tain normal proportion of these elements, properly distributed, 
constitutes vigorous health, and forms a perfect body. If one 
of these elements be in excess, certain forms of disease mani¬ 
fest themselves; if there is not enough, some other malady 
affects the frame. When the blood contains less than its 
healthful amount of iron, it is poor, watery, and compara¬ 
tively colourless; the muscles are flabby, the face pale, the 
eyes sunken, the whole body weak, the mind listless and sad. 
If the bones have not enough lime, they have no strength, are 
easily bent, and the patient is rickety; if there is too much 
lime, then the bones are brittle, and are broken by the slightest 
fall or unusual strain. The highest skill of the physician in 
these cases consists in determining the excess or deficit of any 
element, and in supplying such food or drug as will meet the 
case; when the medical attendant cannot determine what is 
wanting nor furnish the supply, nature is often loud enough 
in her calls, through the tastes or appetites, to indicate very 
clearly what item of food or drink contains the needed ele¬ 
ments; this is the “ Instinct of Appetite. 5 ' Chemistry is 
unable to sav of but one article of human food that it contains 
%> 
all the constituents necessary to supply the human body with 
every element requisite for its welfare, and that is pure milk, 
as supplied by the mother of the new being; but after the 
first years of life the body demands new elements, in order to 
enable it to meet the duties which increasing age imposes; 
